Drag torque of high T-c superconductor magnet bearings with multi-piece ring magnets or superconductors

In order for a superconductor magnet levitation bearing to rotate freely, t he magnetic field from the magnet must be axisymmetric about the axis of ro tation. In contrast, the shape of the superconductor need not be axisymmetr ic. This allows us to make a large ring of high temperature superconductor out of smaller pieces in the fabrication of superconductor magnet bearings. The problem then arises as to whether the substitution of a single large p iece of superconductor by smaller pieces might contribute to additional pow er loss. We have investigated this by studying the drag torque experienced by multi-piece sing magnets as they turn above, multi-piece rings of superc onductors, and comparing with results from single pieces of similar sizes. We have coordinated the variation of the drag torque during a turn with the relative orientation of the magnet and superconductor pieces. We use the m ean value of the drag torque over several turns as a measure of power loss.